The invention relates to a rolling or convoluted boot for a constant velocity universal joint. The constant velocity joint includes an outer joint part and an internal inner joint part with a rotatable shaft. A joint space is formed between the boot and joint parts. The space is sealed towards the outside by the rolling or convoluted boot. Pressure is balanced between the joint space and the surrounding atmosphere by the boot.
Constant velocity universal joints transmit torque in the drive shafts of motor vehicles engine-driven amphibian vehicles and machinery. The joints include a permanent amount of lubricating grease. The joint space is sealed by a convoluted or rolling boot whose purpose is to prevent escape of lubricant and entrance of foreign particles, such as dust or water.
As a result of the heat caused by friction in the course of the operation of the joint, the joint temperature increases, which, in turn, causes an increase in the pressure in the joint space sealed by the convoluted or rolling boot. This increase in pressure leads to boot deformation and, in extreme cases, to the destruction of the boot. To prevent destruction, it is essential to accurately balance the pressure between the joint space and the surrounding atmosphere. Normally, this pressure balance is achieved via an axially extending, permanently open channel. The channel is integrated into the small boot diameter and extends between the boot and the shaft. Such a pressure balancing assembly has proved itself. However, with wading or amphibian vehicles and with road vehicles driving on wet surfaces, there is a risk that as a result of the permanently open aperture, water or dirt may enter into the joint space.
It is the object of the present invention to provide a rolling or convoluted boot for constant velocity universal joints of the initially mentioned type in which a pressure balancing aperture may be closed. According to a first solution, the objective is achieved by a rolling or convoluted boot with at least one pressure balancing aperture located in a pressure balancing region. The pressure balancing region is adapted to be tightly adjoining the shaft when the shaft is at rest, and to lift off radially during shaft rotation as a function of the rotational speed or being supported by a pressure differential between the sealed area and the ambient pressure. An equivalent second solution provides the rolling or convoluted boot with at least one pressure balancing aperture located in a pressure balancing region, with a tightly adjoining sealing element adapted to lift off the shaft during shaft rotation as a function of the speed or being supported by a pressure differential between the sealed area and the ambient pressure. The sealing element is pulled over, or integrally formed with the pressure balancing region.
By introducing these measures it is possible to provide a constant velocity universal joint in which, at low joint speed occurring when the vehicle wades or drives through off-highway territory or is completely stationary, e.g. when the vehicle is afloat, the pressure balancing region tightly rests against and seals the shaft. At higher speeds which occur under normal road conditions the centrifugal force of the boot increases and the sealing element and the boot or the sealing element is lifted off the shaft in its pressure balancing region. At the same time, the centrifugal force prevents water spray or foreign particles from entering the joint space. These measures in accordance with the invention are not restricted to being applied to constant velocity universal joints; they may be applied to all rotating shafts which are surrounded by a boot and which require pressure balancing measures.
In order to ensure that the pressure balancing apertures open and close without fail and as a function of the joint speed and pressure differential without being adversely affected by the grease filling, it is proposed that the pressure balancing region be located axially adjoining the boot fixing region. In the case of the first solution, the pressure balancing region itself effects opening and closing, whereas in the second solution, opening and closing is effected exclusively by the sealing element.
The sealing element functions independently of the boot design and may therefore be used for joints fitted with a convoluted boot and for joints fitted with a rolling boot. It is irrelevant whether the sealing element is connected to the convoluted or rolling boot by a tensioning strip or whether it is a fixed part of the boots. It is advantageous for replacement that the sealing element be designed as a separate component.
From the following detailed description taken in conjunction with the accompanying drawings and subjoined claims, other objects and advantages of the present invention will become apparent to those skilled in the art.